For some young men, the trunk is the perfect spot for a huge set of car speakers.

But brothers Andrew and Chris Ewert have put something far more powerful in the back of their parents' Toyota Prius: a lithium-ion battery pack capable of dramatically boosting the hybrid car's already impressive fuel efficiency.

Unlike a conventional gas-electric Toyota Prius, which gets about 55 to 60 miles per gallon of gas, the Ewerts' so-called "plug-in hybrid" is capable of traveling about 100 miles per gallon.

And it only takes 35 cents' worth of electricity from a standard power outlet to charge the extra batteries.

"We've gotten about a thousand miles off of one tank of gas," Andrew Ewert said. "This is the future of cars. We strongly believe that this is where it's headed."

The Ewerts' modified car was among dozens of alternative fuel vehicles on display Tuesday at an Earth Day event at Wheaton College.

U.S. Rep. Peter Roskam kicked off the event by saying America must end its dependence on foreign oil.

In the 1950s, the U.S. imported about 3 percent of its energy needs. Roskam said the nation now is importing almost 22 percent of its crude oil from other nations.

"Obviously, in an increasingly unstable world, that tends to make us more vulnerable," he said.

Among the energy-efficient vehicles on display during Tuesday's exposition was a battery-powered scooter and a Honda Civic powered by natural gas.

Car buyers apparently don't have to abandon their love of sport utility vehicles to do their part for the environment.

Representatives from General Motors Corp. were showing off a new line of gas-electric hybrid Chevy Tahoes.

"There are still a lot of people with large families," said Richard Gunther Jr., a fleet account executive for GM.

"We also like to camp and do outdoor things," he said. "To be able to be fuel-efficient and still do that, that's the whole idea behind this."

Greg Doty, Wheaton College's director of purchasing, said there's more options for people interested in buying energy-efficient vehicles.

"The way gas prices are going, the public is going to start crying out for other ways to get around," he said.

Last year, only a handful of cars were at the Wheaton College event. This year, about 30 vehicles were on display.

"This market is taking off," Andrew Ewert said. "As people realize that gas prices are going up -- and they're not coming down -- there has to be an alternative to gasoline."

In the meantime, governmental entities such as the DuPage County Forest Preserve District are trying to lead the charge. More than half the district's fleet of vehicles run on alternative fuels.

District President Dewey Pierotti said the hope is to have the entire fleet powered with natural gas, biodiesel, ethanol or propane by 2011.

"The purpose is to improve the quality of the air," Pierotti said. "So we feel it's mandatory that we do this. And we feel that once we do it, everyone else is going to follow along."

Of course, you don't have to spend tens of thousands of dollars on a hybrid vehicle to help the environment.

In Lombard, an Anti-Idling Day event reminded people that they can lower pollution and conserve gas by simply shutting off their cars.

Glenn Westlake Middle School parent Laurel Geoffrey admits she often leaves her car running while waiting to pick up her son.

"I usually don't even think about it and idle my car," she said.

Numerous signs and 15 students handing out educational literature reminded Geoffrey and others to shut their cars off.

Organizers said the goal of Tuesday's effort was to raise awareness that idling produces unnecessary toxic emissions that contribute to a list of health problems, including asthma.

There's also money to be saved.

Idling for an hour burns up to a gallon of fuel, according to Eve Pytel, assistant director of the Clean Air Counts program.

"With gas costing as much as it does, why would you want to just burn it?" she said.

Permanent signs have posted around Lombard to serve as constant reminders.

"We're just hoping to get people on a broader level to realize that this is something for every day," Pytel said, "not just for Earth Day."